ARCHIVED REPORTS XR0011746 - Laserfiche WebLink

Home Browse Search

Report: Groundwater-quality Monitoring—April 15,2003: 7500 West Eleventh Street, Tracy, CA. Page 7 PP =0.83 ` The depression in the elevation of the water table due to the presence of floating product is given by: , j W=T (pp/pw) (Equation 1) ,. i Where: W= the depression of the water table T = the thickness of floating product in the monitoring well pW = the specific gravity of the groundwater pp = the specific gravity of the floating product `1 Thus, in the case of the floating;product measured in well MW-7 on April 15, 2003: i W= 0.52 (0.83/1.0) = 0.43 ft. Accordingly, when drawing the contours shown on Figure 2, the elevation of the { > groundwater in well MW-7 was based on an assumed depth to groundwater of 9.33 ft. rather than the depth of 8.95 ft. actually measured. This yields a corrected groundwater r table elevation of 39.27 ft. MSL (which is shown on Figure 2) compared to the E uncorrected value of 38.84 ft MSL given in Table 1. In addition, the groundwater elevations in Wells MW-3A, MW-3B and MW-12A were _ not considered when the groundwater contours were drawn because, although small in magnitude, differences between the elevations of the groundwater in wells MW-3, MW- 3A and MW-3B and in MW-12 and MW-12A are sufficiently great to indicate that the groundwater monitored by the shallow well at the locations of each of those well clusters has different pieziometric pressures than that of the deeper wells in the same cluster and therefore must be assumed, at least locally, to monitor aquifers different from that monitored by the deeper wells. During the April 15, 2003 sampling round the groundwater level in Monitoring Well 3B, which is screened in an aquifer the top of which is some 37 ft. BGS, was 0.37 ft. lower than that in Monitoring Well 3, which is screened in the shallow, near-surface aquifer. This is consistent with the seasonal onset of agricultural irrigation which causes discharge into the near-aquifer. On April 15, 2003, the mean groundwater gradient in the shallow, near-surface aquifer beneath the site was approximately 0.003 ft/ft. Although there were some minor changes j in the details of the groundwater elevation contours, the direction ofgroundwater flow remained substantially unchanged from the north-northeasterly direction that has r prevailed since depths to groundwater were first measured in May 2000. sic i